Method of sensitizing substrates for chemical metallization

ABSTRACT

There is provided a new process for the production of printed circuits. The process comprises coating a base with a layer of copper, nickel, cobalt or iron salts or salt compositions, which on exposure to radiant energy, such as heat, light, etc., thermal or chemical reducing agents are converted to a layer of metal nuclei that is non-conductive, but which is capable of catalyzing the deposition of metal onto the base from an electroless metal deposition solution in contact with the metal nuclei.

United States Patent Polichette et al.

1*Sept. 23, 1975 METHOD OF SENSITIZING SUBSTRATES FOR CHEMICAL METALLIZATION Inventors: Joseph Polichette, South Farmingdale; Edward J. Leech, Oyster Bay; Francis J. Nuzzi, Lynbrook, all of NY.

[73] Assignee: Photocircuits, Hartford, Conn.

[ Notice: The portion of the term of this patent subsequent toNov. 13, 1990, has been disclaimed.

[22] Filed: Feb. 18, 1972 Appl. No.: 227,446

Related US. Application Data CE4N (IA/GLAD 845E MATERIAL l l ffODI/CE #01. ss

IMMERS' IN PREA C 771 4 7' R [MMERSE IN A CTN 4 70/? awa Era-55s msncr/varok, Acrmrofi. air.

3,562,005 2/1971 De Angelo et al. ll7/l30 E 3,615,732 10/1971 Shipley et al ll7/l30 E 3,627,558 l2/l97l Roger et al. 1 17/47 3,674,485 7/1972 Jonker ct al. 96/362 3,704,208 ll/l972 Russo l 17/47 Primary ExaniinerCharles E. Van Horn Assistant Examiner-Jerome W. Massie Attorney, Agent, or Firm-Morgan, Finnegan, Pine, Foley & Lee

[ 7] ABSTRACT There is provided a new process for the production of printed circuits. The process comprises coating a base with a layer of copper, nickel, cobalt or iron salts or salt compositions, which on exposure to radiant energy, such as heat, light, etc., thermal or chemical reducing agents are converted to a layer of metal nuclei that is non-conductive, but which is capable of catalyzing the deposition of metal onto the base from an electroless metal deposition solution in contact with the metal nuclei.

32 Claims, 21 Drawing Figures IMME'RSE IN CHEM/CALL) REDUC/BLE ME74L SALT 84TH l DRAIN 4ND IMMERSE l/V REDUCE 84TH IMMERSE IN 847' FORM lH/IV ELECWES CU DEFUS'IT IMAGE BACKGROUND 2. puaroflssls r, Sens! PR/rlr av rue-u REMOVE TEMP. H4775? MASK L Posr cues J L DER T GOA 7'' Hum. 1 l FABRICATION l L M'flo Mash/ 6 0/? THE LIKE ILHTE REMOVE MTTERN MSK l QUICK-E 1'? RE- MOVE TWIN GI-F/LM WEE/V marrow FINAL FA BR/CAWOIV US Patent CZEAN (INCL/1D BASE M4 TEE/AL ifnoauc: HOL 55:

JMMERSE nv PREACT/VA 70R IMMERSE IN A C TI VA 70/? IMMERS' E IN REDUCE/Q Sept. 23,1975

Sheet 1 of 20 Aer/warm, etc.

IMMERSE Ml CHEM/CALL! REOUC/BLE METAL SALT 84 TH 4 DAWN AND IMMERSE w R'Dl/CE'R 54TH AVA/5E [MMERSE IN 847' TO FORM I'H/N ELECIPOLESS CU DEPOSIT IMAGE BA CIIG'ROU/VD a PHOTOAES/ST,

C'u ELECTROPZATE T0 DES/RFD THICKNESS REMOVE TEMR PATTERN MAS/f QUICK- 5721/ 70 R5- MOVE m/zv cu-F/uu BETWEEN com/arms THE LIKE PL ATE Alf/40 0A 5/1/ 6 0/? REMOVE PATTERN MASK QUICK-E T6 T0 RE- MOVE THIN fi'U-F/LM BETWEEN Can/00670195 FIG. I

FINAL. FA BRIG A 770 US Patent Sept. 23,1975 Sheet 2 of 20 3,907,621

US Patent Sept. 23,1975 Sheet 3 of 20 3,907,621

US Patent Sept. 23,1975

Sheet 5 of 20 3,907,621

l IMME /N THEE/"ALLY M Hows} R5558 METAL SALT BATH I'M/VERSE //V PREflCTIl/d 70/2 wan/1v AND HIE-47' JgfREDUiE AL 54 IMMERSE IN T ACT/V4 70R [MMEPSE IN BAT/7' 70 FORM IMMERSE IN rl-l/N EL ECTIPOLESF REDUCER CU DEPOS/T I! REMOVE EXCESS IMAGE BACKGPOUIVD PREfiC' TI V4 TOR, 9;]. PHOTUPES/fil; SCREEN ACT/V470, EZC. P/Pl/VT OR THE LIKE REMO VE TEMH &

Cu ELECTPOPlATE T0 MM an Sn/PA 012 THE LIKE PL 47' E REMOVE QUICK -E' TC H TO REMOVE Til/N Cu-F/ZM PA TTERN MASK BETWEEN C'ONDUCTOHS LPGST CURE J 60A 052 T 60A 7 FINAL i l T ..1 FINAL FABRICATION FIG. 5

I l L POST CURE J FINAL. FABR/CA T/ON US Patent Sept. 23,1975 Sheet 6 of 20 3,907,621

(YEA/V UNCLAD I 8455 MATfR/AL IMMERSE RAD/A T/ON PEOUC/BLE ME T4 L. SALT 54 TH L PRODUCE HOLES J'MMERSE nv PREACT/VA 702 MM 11v AND IfiRAD/ATE w/rH e. .uaur, EL Ecr- RON, EAMs, AND men/r5 IMMERSE nv rafieaucs METAL SALT AcT/ v4 TOR 6 muses: m 54TH I'MME'RSE m m FORM TH/IV REDUCE/2 ELE'C'TROLESS Cu aspos/r REMOVE EXCESS IMA GE BJCKGRWND PREAC AC 711 553322. M7718;- Marv/ream;

SCREEN mural? mums DRY C0 ELECTROPLATE 7'0 DES/RED THICKNESS Ali/4a 0R .Sn/Pb OR THE LIKE PLATE FEM 0 VB PATTERN MAE/f &

REMOVE TEMP. PA T FERN MASK u/cn-srcu r0 RE- MOVE THIN Cu-F/LM BETWEEN co/vaucrms QUICK-576W 70 RE- movs mw fill-FILM i asrwzm ca/vaucraRs I" I L 2 32? L P057 CURE} FINAL. i I

FINAL FABR'CA 1 P057 cues J FABRICATION FINAL FA BR/CA T/ON FIG. 6

US Patent CLEAN UNCLAD BASE MATERIAL IMMERSE IN PREAC 7'! VA TOR IMMERSE IN ACTIVATR &

IMMERSE IN REDUCER REMOVE EXCESS PREA r/ma R,

ACT/VATOR, elc.

DRY

heet 7 of r IMMERSE //v IMMERSE IN IMMERSE //v CHEM/(ALLY THERMALLY RADIATION REDl/C/BLE MEIZIL P50061845 METAL REDUCIBLE mam SALT BATH 5447' 84TH .SALTBATH 4 & i ORA/1v AND pen/Iv AND mnwnuammm- I'M/VERSE 11v HEAT 70 1950065 4r: w/m (JG/476k. REOUCER 847/, METAL 5:447 TOREDUCE MEMLSALT RINSE IMAGE BAC'KMfll/A/fl WIT/1 TEMPORA R Y REVERSE M/1 E. PHUTOREJ'IS T,

JZWEEM RINI 0/? THE LIKE SIPED THICKNESS REMOVE TEMP,

L DER CD4 T I L ffif 15 .1

FINAL FABRIC A TION PATTERN MASK FINA L FABRIC! TION FIG] US Patent Sept. 23,1975 Sheet 8 f 3,907,621

04 64M u/vcmo 845E MATERML C04 7" WITH OX/D/ZABLE IMMERSE w IMMERSE IMMERSE RES/Nous FILM CHEM/CA L L Y THERMA L L. Y RAD/A T/ON i REDUC/BLE METAL REOUC/BLE METAL REDUC/BLE METZL '""l SALT BATH SALT BATH SALT BATH :fRODl/CE h'oLL-s' I I DRAIN AND DRAIN AND 024w 4w Teena/- IMMERSE IN HEAT To REDUCE ATE WlTHL/GHTevc. OX/D/ZE REOUCER BATH METAL SALT mEEwcEMmL sm L r l w RINSE I R5006 I I I I .r ms gss w BATH OHM THIN i ELECTROLESSCL/DEMSIT L MM EAaraEaw/o WITH TEMPORARY REVERSE MAs/r-e. uaraeL-s/szsce L-w PRINT OR THE LIKE 3 a, EL EcTeaPM-TE r0 THE ass/Rea THICKNESS REMOVE Alf/4LT 0e S'n/PA PATTERN MASK 0e THE LIKE PLATE QUICK-ETC RE- i move THIN E/LM Ber- REMOVE ween couaucmns RJTTERA/ MASK L 4 all/671 .676 T0 r-- 1 AEMOVE THIN I PosT CURE I .SOLDER FILM BETWEEN l T .l C04 7- COA/DUCTORS' FINAL L r- 1 FABRICATI P057 c095] L'FP EK Q I FlMd-L F/AML. FABR/CA TIONV FABHCAT/o US Patent Sept. 23,1975 Sheet 9 0f 20 3,907,621

US Patent Sept. 23,1975 Sheet .10 of 20 3,907,621

male

1 I I l US Patent Sept. 23,1975 Sheet 11 of 20 3,907,621

FIG.||

US Patent Sept. 23,1975 Sheet 12 of 20 3,907,621

CLEAN UNCLAD BASE MATERIAL I C047 WITH V 0x10124545 IMMERSE //v J'MMERSE //v IMMERSE 11v RES/N005 FILM CHEM/CALLY THEE/WALL) RADIATION i P5000515 MEML 25000545 M6744 Real/15m METAL 541.7 BATH SAATBATH SALT BATH :fRODUCE HOLES I RA/1v AND (MAW AND 004/ mp 14mm IMMEASE nv HEAT TOE-Paws ATE W/fi/ uavret. OXlD/ZE 9500651? 5427/ MErAL .SZILT 7a PEWCEAIEMZ SALT R/NSE I REDUCE L. l l

I IMAGE RINSE BA CKG'EOU/VD AND DRY WITH FEM/DEAR! RV25E MASK nsc 72045554? Cu RATE 0/ m ass/ps0 WWI/55's REMOVE TEMP. PA rraeu MASK I 50405;? P057 J coAT I 5555a m I -v- FAee/cnr/o/v FINAL FABRICATION FIG. [2

US Patent Sept. 23,1975 Sheet 13 of 20 3,907,621

FIG. I3

US Patent Sept. 23,1975 Sheet 14 of20 3,907,621

US Patent Sept. 23,1975 Sheet 16 of 20 3,907,621

FIG. [6

US Patent Sept. 23,1975

Sheet 17 of 20 FIG.I7

US Patent Sept. 23,1975 Sheet 18 of 20 3,907,621

US Patent Sept. 23,1975 Sheet 19 of 20 3,907,621

THIN C u- C140 BASE MA F9/4L PRODUC E HOLES IMMERSE IN IMMERSE //v IMMERSE //v mam may eam- T/IBPMALLY REDUC/BLE PAD/4770A! PEOUC/BLE ME7I4L SALT BATH METAL SALTBATH M57741. SALT BATH J J & ORA/N 4N0 0/?A/A/ Aflb DEA/N AND IMMERSE IN #647 To REDUCE mew/A75 r0 REDUCE/i BATH METAL .SALT 50005 M51214 $447 4 RINSE IMAGE BQCKGROUIVD WITH YEMPORARY REVERSE MASK ELECTROLESSLY Cu PLATE UP TO 055/950 m/cm/m" 0 an E ECTIPOPLA 7's AND 09 M740 o2 v/Pb e14:- (NON- Cu) PEA TE 6 REMOVE PATTERN MAS/r Qu/or-Ercw 10 RE- uave COPPER earwez-w C'ONOOUDQS 

1. IN A PROCESS FOR MAKING PRINTED CIRCUIT BOARDS, A SENSITIZATION PROCEDURE WHEREIN THE STEPS CONSIST ESSENTIALLY OF APPLYING A SOLUTION CONTAINING A REDUCIBLE SALT OF A NON-NOBLE METAL OF THE GROUP CONSISTING OF METALS OF PRIOD 4 OF GROUPS IB AND VIII OF THE PERIODIC TABLE OF ELEMENTS DIRECTLY TO A SURFACE OF AN INSULTING BASE AND OF REDUCING SAID SALT BY A TECHIQUE OF THE GROUP CONSISTNG OF THERMAL REDUCTION, REDUCTION BY RADIATION AND REDUCTION WITH CHEMICAL REDUCING AGENTS TO FORM A NON-CONDUCTIVE LAYER OF FREE METALLIC NUCLEI OF SAID METAL ON SAID SURFACE, SAID NUCLEI BEING CATALYTIC FOR THE DEPOSITION OF
 2. A process as defined in claim 1 where said base has been pretreated to: a. preactivate the surface by contacting said surface with an organic liquid which is capable of being imbibed by the surface to render the surface temporarily polar and wettable b. activate the surface by contacting said surface with an oxidizing agent to render it permanently polar and wettable c. reduce excess oxidizing agent with a reducing agent and d. rinse said surface.
 3. A process as defined in claim 1 wherein the compound is reduced by chemical means.
 4. A process as defined in claim 1 wherein the compound is reduced by thermal means.
 5. A process as defined in claim 1 wherein the compound is reduced by radiation means.
 6. A process as defined in claim 1 wherein the printed circuit pattern is fOrmed by placing a photoresist background circuit mask on the surface, electrolessly depositing a metal on the exposed area and thereafter removing the photoresist background circuit mask.
 7. A process as defined in claim 2 wherein an adhesive film having dispersed rubber particles is coated on the insulating base prior to pretreatment.
 8. A process as defined in claim 1 wherein the insulating base is clad with a thin metal laminate and holes are formed prior to providing such base with non-conductive free metallic catalytic nuclei.
 9. A process as defined in claim 1 wherein said base is opaque or has been rendered opaque to the transmission of radiant energy.
 10. A process as defined on claim 1 wherein said solution is applied to preselected areas of said base.
 11. A process as defined in claim 1 wherein said salt is a salt of an acid and a metal of the group consisting of copper, nickel, cobalt and iron.
 12. A process as defined in claim 1 wherein said salt solution also contains an auxiliary reducing compound.
 13. A process for making a printed circuit board which comprises: a. treating a base material having a non-polar surface with a pre-activating compound or composition which consists essentially of an organic liquid capable of being imbibed by the surface to render the surface temporarily polar and wettable; b. treating the pre-activated base material with an oxidizing agent; c. treating the pre-activated, oxidized base material with a reducing agent; d. treating the base to remove excess oxidizing and reducing agents; e. drying the base or draining the base; f. treating the base by a sensitization procedure wherein the steps consist essentially of applying a solution containing a reducible salt of a non-noble metal of the group consisting of metals of Period 4 of Groups IB and VIII of the Periodic Table of Elements directly to a surface of the base, of drying the base or draining the base, and of reducing said salt by a technique of the group consisting of thermal reduction, reduction by radiation and reduction with chemical reducing agents to form a non-conductive layer of free metallic nuclei of said metal on said surface, said nuclei being catalytic for the deposition of electroless metal; g. rinsing the base; h. forming a circuit pattern by placing a photoresist background mask on the surface; i. electrolessly plating the circuit pattern with a metal up to the desired thickness; j. removing the temporary pattern mask to produce the unmasked printed circuit board.
 14. A process as defined in claim 13 including the step of producing at least one hole in the base before the preactivation step (a).
 15. A process as defined in claim 13 including the subsequent step of solder coating to produce a printed circuit board having a layer of solder on the conductor lines.
 16. A process as defined in claim 14 including the subsequent step of solder coating to produce a printed circuit board having a continuous layer of solder on the conductor lines and on the layer of metal in the hole walls in the printed circuit board.
 17. A process for making a printed circuit board which comprises: a. coating an insulated base with an oxidizable adhesive film; b. treating the adhesive film with an oxidizing agent; c. treating the surface with a reducing agent to remove excess oxidizing agent; d. drying the base or draining the base; e. treating the base by a sensitization procedure wherein the steps consist essentially of applying a solution containing a reducible salt of a non-noble metal of the group consisting of metals of Period 4 of Groups IB and VIII of the Periodic Table of Elements directly to a surface of the base, of drying the base or draining the base, and of reducing said salt by a technique of the group consisting of thermal reduction, reduction by radiation and reduction with chemical reducing agents to form a non-conduCtive layer of free metallic nuclei of said metal on said surface, said nuclei being catalytic for the deposition of electroless metal; f. rinsing the base; g. forming a circuit pattern by placing a photoresist background mask on the surface of the base; h. electrolessly plating the circuit pattern with a metal up to the desired thickness; and i. removing the temporary pattern mask to produce the unmasked printed circuit board.
 18. A process as defined in claim 17 including the subsequent step of solder coating to produce a printed circuit board having a layer of solder on the conductor lines.
 19. A process as defined in claim 17 including the step of producing at least one hole in the base before oxidizing step (b).
 20. A process as defined in claim 19 including the additional step of solder coating to produce a printed circuit board having a continuous layer of solder on the conductor lines and on the layer of metal in the hole walls in the printed circuit board.
 21. A process for making a printed circuit board which comprises: a. producing holes in an insulating base which is covered with a thin layer of conductive metal; b. treating exposed surfaces of said base by a sensitization procedure wherein the steps consist essentially of applying a solution containing a reducible salt of a non-noble metal of the group consisting of metals of Period 4 of Groups IB and VIII of the Periodic Table of Elements directly to the surface of the base and of reducing said salt by a technique of the group consisting of thermal reduction, reduction by radiation and reduction with chemical reducing agents to form a non-conductive layer of free metallic nuclei of said metal on said surface, said nuclei being catalytic for the deposition of electroless metal on the exposed surfaces of said base; c. forming a circuit pattern by placing a photoresist background mask on the surface of the base; d. electrolessly plating the circuit pattern with a metal up to the desired thickness; e. removing the temporary pattern mask; f. quick-etching the base to remove the thin metal layer between the conductors to produce the printed circuit board.
 22. A process as defined by claim 21 which includes the subsequent step of solder coating to produce a printed circuit board having a layer of solder on the conductor lines.
 23. A process for making a printed circuit board which comprises: a. coating an insulating base with an adhesive film having dispersed therein a material which is catalytic to the reception of electroless metal and activating the film; b. forming a circuit pattern by placing a photoresist background mask on the surface of the base; c. electrolessly plating a metal on the exposed surface of the circuit pattern up to the desired thickness; d. coating the circuit board with a permanent solder mask; e. producing one or more holes through the base at a predetermined loci; f. treating exposed surfaces of the base by a sensitization procedure wherein the steps consist essentially of applying a solution containing a reducible salt of a non-noble metal of the group consisting of metals of Period 4 of Groups IB and VIII of the Periodic Table of Elements directly to a surface of the base and of reducing said salt by a technique of the group consisting of thermal reduction, reduction by radiation and reduction with chemical reducing agents to form a non-conductive layer of free metallic nuclei of said metal on said surface, said nuclei being catalytic for the deposition of electroless metal on the surface of the walls of the holes; g. rinsing the base; and h. electrolessly plating the walls of the holes with a metal up to the desired thickness to produce the printed circuit board.
 24. A process as defined in claim 23 including the subsequent step of solder coating to produce a printed circuit board which has a permanent solder mask over the circUit pattern and a layer of solder in the walls of the plated through holes.
 25. A process for making a printed circuit board which comprises: a. coating an insulating base with an adhesive film having dispersed therein a material which is catalytic to the reception of electroless metal and activating the film; b. forming circuit pattern by placing a photoresist background mask on the surface of the base; c. electrolessly plating a metal on the exposed surface of the circuit pattern up to the desired thickness; d. temporarily masking the total surface of the base; e. producing one or more holes through the base at predetermined loci; f. treating the masked base by a sensitization procedure wherein the steps consist essentially of applying a solution containing a reducible salt of a non-noble metal of the group consisting of metals of Period 4 of Groups IB and VIII of the Periodic Table of Elements directly to a surface of the base, of drying the base or draining the base, and of reducing said salt by a technique of the group consisting of thermal reduction, reduction by radiation and reduction with chemical reducing agents to form a non-conductive layer of free metallic nuclei of said metal on said surface, said nuclei being catalytic for the deposition of electroless metal on the surface of the walls of the holes; g. rinsing the base; h. electrolessly plating the walls of the holes with a metal up to the desired thickness; and i. removing the temporary mask to produce the printed circuit board.
 26. A process as defined in claim 25 including the subsequent step of solder coating to produce a printed circuit board having a layer of solder over the conductor lines and on the walls of the plated through holes.
 27. A process for making a printed circuit board which comprises: a. coating an insulating base with an oxidizable adhesive film having dispersed therein a material which is catalytic to the reception of electroless metal and activating the film; b. temporarily masking the total surface of the base; c. producing one or more holes in the base at predetermined loci; d. treating the masked base by a sensitization procedure wherein the steps consist essentially of applying a solution containing a reducible salt of a non-noble metal of the group consisting of metals of Period 4 of Groups IB and VIII of the Periodic Table of Elements directly to a surface of the base, of drying the base or draining the base, and of reducing said salt by a technique of the group consisting of thermal reduction, reduction by radiation and reduction with chemical reducing agents to form a non-conductive layer of free metallic nuclei of said metal on said surface, said nuclei being catalytic for the deposition of electroless metal on the surface of the walls of the holes; e. rinsing the base; f. removing the temporary mask; g. forming a circuit pattern by placing a photoresist background mask on the surface of the base; h. electrolessly plating the walls of the holes and pattern up to the desired thickness; i. electrolessly plating the exposed circuit pattern with a second metal up to the desired thickness; and j. removing the pattern mask to produce the printed circuit board.
 28. A process for making a printed circuit board which comprises: a. pre-activating a normally non-polar insulating base by contacting the surface of said base with an organic liquid which is capable of being imbibed by the surface to render the surface temporarily polar and wettable; b. activating the surface with an oxidizing agent to render it premanently polar and wettable; c. reducing excess oxidizing agent with a reducing agent; d. rinsing the surface; e. drying the insulating base; f. treating the base by a sensitization procedure wherein the steps consist essentially of applying a solution containing a reducible salt of a non-noble metal of the group consisting of metals of Period 4 of Groups IB and VIII of the periodic Table of Elements directly to a surface of the base and of reducing said salt by a technique of the group consisting of thermal reduction, reduction by radiation and reduction with chemical reducing agents to form a non-conductive layer of free metallic nuclei of said metal on said surface, said nuclei being catalytic for the deposition of electroless metal; a. rinsing the base; h. electrolessly depositing a thin layer of metal on the surface of the base; i. forming a circuit pattern by placing a photoresist background circuit mask on the surface; j. electrolessly plating the exposed circuit pattern; k. removing the photoresist background circuit mask; and l. quick-etching the base to remove the thin metal layer between the conductors to produce said printed circuit board.
 29. In a process for making printed circuit boards, a sensitization procedure wherein the steps consist essentially of applying a solution containing a reducible copper salt directly to a surface of an insulating base and of reducing said salt with a chemical reducing agent to form a non-conductive layer of free copper nuclei on said surface, said nuclei being catalytic for the deposition of electroless metal; and thereafter selectively metallizing the sensitized surface of said base.
 30. In a process for making printed circuit boards, a sensitization procedure wherein the steps consist essentially of applying a solution containing a reducible copper salt directly to a surface of an insulating base and reducing said salt by thermal reduction to form a non-conductive layer of free copper nuclei on said surface, said nuclei being catalytic for the deposition of electroless metal; and thereafter selectively metallizing the sensitized surface of said base.
 31. In a process for making printed circuit boards, a sensitization procedure wherein the steps consist essentially of applying a solution containing a reducible copper salt directly to a surface of an insulating base and of reducing said salt by radiation to form a nonconductive layer of free copper nuclei on said surface, said nuclei being catalytic for the deposition of electroless metal; and thereafter selectively metallizing the sensitized surface of said base.
 32. A process for making a printed circuit board which comprises: a. preactivating a normally non-polar insulating base by contacting the surface of said base with an organic liquid which is capable of being imbibed by the surface to render the surface temporarily polar and wettable; b. activating the surface with an oxidizing agent to render it permanently polar and wettable; c. reducing excess oxidizing agent with a reducing agent; d. rinsing the surface; e. drying the insulating base; f. immersing the base in a solution of a nonnoble metal salt compound selected from the metals of the group consisting of copper, nickel, cobalt, tin and iron which is chemically reducible to form a non-conductive deposit of freemetallic nuclei which are catalytic to the reception of electroless metal; g. reducing said chemically reducible non-noble metal salt compound by thereafter treating the insulating base with a chemical reducing agent to form a layer of non-conducting metal nuclei and thereafter rinsing the base; h. electrolessly depositing a thin layer of metal on the surface of the base; i. forming a circuit pattern by placing a photoresist background circuit mask on the surface; j. electrolessly plating the circuit pattern; k. removing the photoresist background circuit mask; and l. quick-etching the base to remove the thin metal layer between the conductors to produce said printed circuit board. 